1. Field of the Invention
The disclosure relates to a method and apparatus for producing super radiant laser in a half wavelength thick organic semiconductor microcavity.
2. Description of Related Art
Microcavity lasers that utilize solid state organic semiconductors as the gain medium hold promise for a wide range of applications, including chemical sensors and single molecule detectors for biological applications. Such devices also serve as a platform for investigating fundamental physical phenomena such as energy transfer and room temperature condensation of excitons, and a test-bed for developing electrically pumped solid state organic lasers. The very large absorption cross sections of organics suggest that these materials may also be useful as part of communications switching elements and compact sources of non-classical light (e.g., quantum optics).
A number of research groups investigated the lasing properties of organic laser dyes in optical microcavities. The laser dyes were dissolved in solutions which were then flowed into the space between two dielectric (sputter-coated) minors. The spacing between the minors was adjusted either through piezoelectric nano-positioners or through metal spacer layers of precision thickness, such that the gain region thickness had a value equal to λ/2n or an integer multiple thereof.
One observation was an anomalously low lasing threshold, which was attributed to XYZ/super-radiance physical effects and even reported “thresholdless” lasing in the device which had λ/2n thick gain region. The lack of a distinct threshold in the input-output power dependence of the λ/2n has been confirmed. They also determined that there was nevertheless a clear threshold associated with the polarization of the emitted light and that above a given pump pulse energy, the polarization of the emitted light followed the polarization of the pump laser.
In the late 1990's, researchers began developing organic-based microcavity lasers using solid state materials. For example, lasing was achieved in a metal dielectric Bragg reflector (“DBR”) based microcavity that contained the laser dye molecule 4-dicyanomethylene-2-methyl-6-p-dimethylamino-styryl-4H-pyran (“DCM”) as the gain material which was doped into an Alq3 host matrix. The Alq3 host was optically pumped with a 337 nm Nitrogen laser, which in turn excited the DCM molecules via the so-called Forster resonance energy transfer (“FRET”). The gain layer thickness needed to be on the order of 1.5λ/n to provide sufficient gain in order to reach a threshold, which was measured to be 0.3 mJ/cm2. Lasing with the fluorescent conjugated polymer PPV in an all dielectric (2 DBR based) λ/2n microcavity showed 80% polarized emission above a threshold of 15 μJ/cm2. The reduced threshold was attributed to the high quality factor (“Q”) of the microcavity (i.e., Q value of about 1200).
More recently, Alq3:DCM gain layer with thickness of about 1.5λ/n was integrated into an all dielectric microcavity and demonstrated lasing with a threshold of 20 μJ/cm2, using a frequency doubled pulsed Ti:Sapphire laser. The reduction in threshold compared to the metal-DBR based microcavity described above can be attributed to the high Q of the all-dielectric microcavity (i.e., Q of about 4500). There remains a need for a microcavity lasing device with Q value which can overcome the optical losses and achieve lasing. There is also a need for a method and apparatus to reduce the Q value.